The use of whitening agents to impart a greater degree of white in products such as paper, cardboard, fabrics and non-wovens is well known. The most widely used whitening agents in paper and cardboard industry are the derivatives of 4,4′-bis-[1,3,5-triazinyl]-diaminostilbene-2,2′-disulfonic acid substituted at the triazine ring with aniline groups and alkanolamine groups. The aniline groups may in turn contain other sulphonic groups which however, by increasing the solubility in water of the molecules, reduce their affinity towards the cellulose fibers that form the paper and tissues and lead to lower performance in terms of degree of white.
For reasons of ease of processing, the paper industry requires that these whitening agents are supplied in liquid forms of fluid aqueous dispersion or, most preferably, of an aqueous solution stable for at least several months at temperatures from 5 to 40° C.
The stilbene whitening agents that are derivatives of 4,4′-bis-[1,3,5-triazinyl]-diaminostilbene-2,2′-disulfonic acid substituted at the triazine ring with aniline groups and alkanolamine groups, preferred in this field, are not easily soluble in water, therefore the production of the related concentrated and stable aqueous solutions has required in the past the addition of significant amounts, even up to 30%, of additives such as solubilizers, for example urea, caprolactam, ethylene glycol and polyglycols.
However, the added solubilizers do not have great affinity for cellulose and do not contribute significantly to the performance of the product thus resulting, at the end of the process of paper production, in unwanted pollutants. For example, when whitening agents are used in solutions formulated with urea, a heavy pollutant load of nitrogen byproducts and ammonia is introduced in the liquid effluents of the process.
A further problem derives from the inevitable presence of inorganic chlorides in the whitening agent solutions, for example sodium chloride, which is derived from the processes of synthesis of whitening agents themselves. In fact, all industrial processes of production of triazine substituted stilbene whitening agents, require the use of cyanuric chloride as reagent, whose reaction in successive stages with different necessary amino products inevitably leads to the generation of large quantities of inorganic chlorides that are difficult to eliminate.
The inorganic chloride residues generate instability in concentrated aqueous solutions of whitening agents and therefore has been so far indispensable to significantly reduce the content thereof, by inevitably resorting to costly separation osmotic techniques, for obtaining compositions stable over time.
GB 1356016 describes a method for the optical whitening of paper through the use of substantially aqueous suspensions of a compound having the following formula:

wherein M and M1 represent hydrogen, an alkali metal, an alkaline earth metal or ammonium.
U.S. Pat. No. 3,012,971 describes compositions for whitening paper consisting of aqueous solutions of concentrated acid, 4,4′-bis-[2-phenylamino-4-dietanolamino-1,3,5-triazinyl]-diaminostilbene-2,2′-disulfonic acid or of a salt thereof in admixture with alkanolamines, wherein the proportion by weight of alkanolamines compared to whitening agents varies from 0.5:1 to 3.0:1. Since the molecular weight of the alkanolamines is much lower than that of the whitening agents, this interval reflects a large excess of alkanolamine compared to the whitening agent. However, such high quantities of alkanolamines, compared to the whitening power of the composition, are not acceptable from the ecological point of view.
WO 2005/028749 describes aqueous compositions comprising stilbene whitening agents and alkanolamines. This document does not describe any example of a composition comprising a tertiary alkanolamine. Furthermore, it is not mentioned the problem of the effect of the inorganic chlorides on the stability of the solution.
U.S. 2010/0159763 describes aqueous compositions of fluorescent whitening agents substituted at the triazine rings by propionamide amino groups, having the following formula:

in which at least 25% of the ions [M+] associated with the sulfonic group have been replaced by (CH3)2NH+CH2CH2OH ions. However, in such compositions it is necessary to reduce the content of inorganic salts with suitable osmosis processes in order to guarantee the stability of the formulation.
U.S. Pat. No. 4,112,226 and GB 1286459 describe methods for the removal of triazine derivative impurities from fluorescent whitening agents. In fact these impurities, if present in a too high concentration, make the fluorescent whitening agent not suitable for use in the detergent compositions described in those publications, by causing colors and odors of the detergent compositions themselves. The methods described in these documents are based on a boiling step of the impure fluorescent whitening agents in alkaline or alcoholic aqueous solutions and subsequent filtration step of the insoluble whitening agent. However, the described methods do not allow to reduce the content of residual impurities in the agent whitening to below about 2000 ppm. Furthermore, the stability problem of the aqueous solutions of the fluorescent whitening agents is not considered nor tackled.